Abstract:sewage,a particle analyzer was used to measure the particle size distribution of influent of three typicaldomestic sewage treatment plants.The change of particle size distribution and sedimentationperformance were compared by sedimentation experiment. The effect of grit setting on particles removalwas analyzed. The basic characteristics of particle size distribution and the general rules ofsedimentation in typical domestic sewage were obtained. The results show that the median diameter ofparticles in the influent is 8~14 μm,but decreases to 4~8 μm after sedimentation. The total number ofparticles does not decrease,but the particle size decreases. The median diameter of particles after gritsetting is 9~15 μm,but decreases to 4~12 μm after sedimentation. According to the particle size dis⁃tribution before and after grit setting,grit setting has no significant removal effect on particles with parti⁃cle size less than 50 μm. Close-